CN114667165A

CN114667165A - Measuring fluid flow associated with a dialysis machine

Info

Publication number: CN114667165A
Application number: CN202080076970.3A
Authority: CN
Inventors: K·S·普拉西
Original assignee: Fresenius Medical Care Holdings Inc
Current assignee: Fresenius Medical Care Holdings Inc
Priority date: 2019-11-05
Filing date: 2020-11-02
Publication date: 2022-06-24
Also published as: CA3158560A1; EP4054667A4; US20210128809A1; US11452801B2; EP4054667A1; WO2021091832A1

Abstract

A dialysis machine (e.g., a Peritoneal Dialysis (PD) machine) can include a control unit configured to monitor an amount of fluid drawn from a heater bag line during a PD treatment. A processor in the control unit is configured to operate the first pump to draw fluid into the first pump chamber and to measure a first fluid volume in the first pump chamber. The processor is also configured to operate the first and second pumps to transfer fluid from the first pump chamber to a second pump chamber, measure a second fluid volume in the second pump chamber, and determine a measured fluid volume for a single pump cycle based on the first fluid volume and the second fluid volume. The first fluid volume is related to the second fluid volume, and therefore, the plurality of independent measurements increases the accuracy of the fluid volume measurement.

Description

Measuring fluid flow associated with a dialysis machine

Background

Dialysis is a treatment used to support patients with renal insufficiency. The two main treatment options are Hemodialysis (HD) and Peritoneal Dialysis (PD). During hemodialysis, the patient's blood is removed, for example, via an Arteriovenous (AV) fistula or other method (e.g., AV graft), and passed through a dialyzer of a dialysis machine, while also passing a dialysis solution, referred to as dialysate, through the dialyzer. A semi-permeable membrane in the dialyzer separates the blood within the dialyzer from the dialysate and facilitates the exchange of waste products (e.g., urea, creatinine, potassium, etc.) between the blood stream and the dialysate. The membrane prevents blood cells, proteins and other vital components in the blood stream from migrating into the dialysis solution. The cleaned blood flow is then returned to the patient. Thus, the dialysis machine acts as an artificial kidney to clean blood for patients with renal insufficiency.

In contrast to hemodialysis, peritoneal dialysis treatment protocols pump dialysate into a patient's peritoneal cavity, which is the region between the peritoneum and the visceral peritoneum of the abdominal wall in the abdomen (e.g., the space between the membrane surrounding the abdominal wall and the membrane surrounding the internal organs in the abdomen). The lining of the patient's peritoneum acts as a semi-permeable membrane, facilitating waste exchange between the blood stream and the dialysate, functioning similarly to the membrane in the dialyzer of a hemodialysis machine. Over multiple PD cycles, the patient's peritoneal cavity is drained and filled with fresh dialysate.

Automated PD machines, sometimes referred to as PD cyclers, are designed to control the PD treatment process so that it is performed at home without clinical staff, usually while the patient is asleep overnight, to minimize interference with the patient's life. This process is known as continuous cycler assisted peritoneal dialysis (CCPD). Many PD cyclers are designed to automatically fill, dwell, and drain dialysate from the peritoneal cavity. PD treatment usually lasts for several hours, usually starting from an initial drain phase, to empty the used or spent dialysate left in the peritoneal cavity at the end of the last PD treatment. This sequence then proceeds through the progression of the filling, dwell and drain phases followed in sequence. A set of sequential filling, dwell and drain phases may be referred to as a PD cycle.

One aspect relating to the operation of a PD cycler is the determination of the amount of dialysate that has been processed by the machine to provide a rough estimate of the progress of the treatment. However, current methods of determining the amount of dialysate remaining in a dialysate bag can suffer from various inaccuracies.

Disclosure of Invention

A system for performing dialysis treatment is provided. In one embodiment, the dialysis system is a PD system. The PD system may include a plurality of pumps, a cassette, and a processor. The cassette includes a plurality of pump chambers, each pump chamber fluidly connected to a corresponding pressure chamber. The processor is configured to operate the first pump to draw fluid into a first pump chamber fluidly connected to the first pressure chamber and to measure a first fluid volume in the first pump chamber. The processor is also configured to be capable of operating the first and second pumps to transfer fluid from the first pump chamber to a second pump chamber fluidly connected to a second pressure chamber, measure a second fluid volume in the second pump chamber, and determine a measured fluid volume for a single pump cycle based on the first and second fluid volumes.

In one embodiment, each pump includes a piston configured to be engageable with a corresponding pump chamber to increase or decrease the volume of the corresponding pump chamber. Measuring the volume of fluid in the corresponding pump chamber is performed by extending the piston to reduce the volume in the corresponding pump chamber, monitoring a pressure signal from a pressure transducer configured to measure the pressure of fluid in the corresponding pressure chamber, reading the position of the piston at a time indicated by the pressure signal, and converting the position of the piston to a measured volume of fluid.

In one embodiment, determining the measured fluid volume for a single pump cycle is performed by determining a difference between the first fluid volume and the second fluid volume, comparing the difference to a threshold, and if the difference is below the threshold, calculating an average of the first fluid volume and the second fluid volume as the measured fluid volume, or if the difference is above the threshold, setting an alarm.

In one embodiment, fluid is drawn from a heater bag line coupled to the cartridge. The processor is further configured to be able to accumulate the measured fluid volume in a total fluid volume variable to monitor a total amount of fluid drawn from the heater bag line, determine that the total amount of fluid drawn from the heater bag line is above a threshold, and configure the cartridge to draw fluid from a second line to transfer additional fluid to the heater bag line.

In some embodiments, a method for measuring fluid flow through a PD cycler is performed by operating a first pump to draw fluid into a first pump chamber of a cassette, measuring a first fluid volume in the first pump chamber, operating the first and second pumps to transfer fluid from the first pump chamber to a second pump chamber of the cassette, measuring a second fluid volume in the second pump chamber, and comparing the first fluid volume to the second fluid volume to determine a measured fluid volume for a single pump cycle. A computer-readable storage medium storing instructions for performing the above-described method is also disclosed.

In one embodiment, the plurality of pumps may include at least three pumps. In such embodiments, the processor may be further configured to operate the second pump and the third pump to transfer fluid from the second pump chamber to a third pump chamber fluidly connected to a third pressure chamber, measure a third fluid volume in the third pump, and calculate an average of the first fluid volume, the second fluid volume, and the third fluid volume as the measured fluid volume.

Drawings

Fig. 1 illustrates a Peritoneal Dialysis (PD) system according to some embodiments.

Fig. 2 is a perspective view of a PD machine and a PD cassette of the PD system of fig. 1, in accordance with some embodiments.

Fig. 3 is a perspective view of an open cassette compartment of the PD machine of fig. 1, in accordance with some embodiments.

Fig. 4 is an exploded perspective view of the PD cassette of fig. 2, in accordance with some embodiments.

Fig. 5 is a cross-sectional view of the fully assembled PD cassette of fig. 2, according to some embodiments.

Fig. 6 and 7 are perspective views of the PD cassette of fig. 2 from the front and back, respectively, in accordance with some embodiments.

Fig. 8 illustrates a PD cassette resting on a cassette interface according to some embodiments.

Fig. 9A-9G are cross-sectional views of a PD system at various stages of setup, perfusion, and treatment, according to some embodiments.

Fig. 10 illustrates a path between a patient and a PD machine while the patient is receiving PD therapy, in accordance with some embodiments.

Fig. 11A-11F illustrate a fluid flow path from a heater bag line to a patient line through a cassette according to some embodiments.

Fig. 12 is a flow diagram of a method for measuring fluid flow in a peritoneal dialysis machine according to some embodiments.

FIG. 13 is a flowchart of steps for determining a measured fluid volume according to some embodiments.

Fig. 14 is a flow diagram of a method for monitoring total fluid volume in a dialysate bag according to some embodiments.

FIG. 15 illustrates an exemplary computer system according to some embodiments.

Detailed Description

Peritoneal Dialysis (PD) machines can be designed to measure the amount of fluid drained from a dialysate bag in order to detect when the dialysate source may become low. This information can be used to suspend PD therapy when the patient or caregiver changes dialysate bags, sets an alarm of the PD cycler, or fills the heater bag with a reserve fluid in a backup dialysate bag connected to the PD cycler.

One conventional technique for measuring the amount of fluid remaining in a heater bag uses a weighing element positioned below a tray designed to hold the heater bag. The weighing element generates a signal that is converted into the weight of the tray and heater bag. Assuming that the weight of the tray and the weight of the heater bag without liquid remain the same, the weights can be used to infer how much fluid is in the heater bag. However, this technique has its limitations. First, there is no way to prevent a caregiver or patient from placing additional weight on the tray when PD treatment is effective. For example, a patient may place a book or other item on top of the tray during treatment, which may cause the PD cycler to infer that the amount of dialysate in the heater bag is incorrect. Second, the measured weight cannot be used for any critical operations of the PD cycler that rely on knowing the amount of fluid in the heater bag, given that the confidence that the measured weight represents the actual amount of dialysate on the tray is low, and may be the weight of foreign matter on the tray. Thus, the use of this information may currently be limited to setting an alarm to notify the caregiver/patient that the dialysate bag may need to be replaced.

The implementation of weighing cells in PD cyclers is costly and, as mentioned above, provides limited utility because the accuracy of the information cannot be ensured. Thus, new PD cyclers may omit the weighing element in order to reduce the cost of the PD cycler. One technique for indirectly monitoring the amount of fluid in the heater bag is to monitor the amount of fluid that has been pumped from the heater bag. By subtracting the volume of dialysate that has been pumped from the heater bag, and knowing the volume of fluid initially contained in the heater bag, an estimate of the volume of fluid remaining in the heater bag can be calculated. The accuracy of the estimate depends on the accuracy of the measurement of the volume of fluid withdrawn from the heater bag.

One technique for measuring the volume of fluid pumped from a heater bag uses the volume of the pump chamber of the cassette and a pressure transducer that measures the fluid pressure in the pump chamber of the cassette. The combination of the position of the piston head of the membrane attached to the pump chamber and the signal representative of the fluid pressure in the pump chamber can be used to estimate the volume of fluid in the pump chamber after each stroke of the piston. Thus, the PD cycler indirectly measures the volume of fluid passing through the pump chamber during each stroke of the piston. One way to improve the accuracy of such measurements is to pass the same volume through multiple pump chambers, thereby making multiple measurements using different pressure transducer signals and pistons. A combination of multiple independent measurements can be used to estimate the fluid volume with high accuracy, which can be used to replace the function of conventional weighing cell measurements of conventional PD cyclers.

Fig. 1 illustrates a Peritoneal Dialysis (PD) system 100 according to some embodiments. The PD system 100 may include a PD machine 102, which may alternatively be referred to as a PD cycler, disposed on a cart 104. The PD machine 102 includes a housing 106, a door 108, and a cassette interface 110 that contacts a disposable PD cassette 112 when the cassette 112 is disposed within a cassette compartment 114 formed between the cassette interface 110 and the closed door 108. Cassette compartment 114, cassette interface 110, and cassette 112 are shown in more detail in fig. 2. A heater tray 116 is positioned on top of the housing 106. The heater tray 116 is sized and shaped to hold a PD solution bag, such as dialysate (e.g., a 5-liter dialysate bag). The PD machine 102 also includes a user interface such as a touchscreen display 118 that may be operated by a user (e.g., a caregiver or patient) and additional control buttons 120 to allow, for example, setting, initiating, and/or terminating PD therapy. The systems and techniques described herein are primarily discussed in connection with a particular type of PD machine. However, it should be noted that the systems and techniques described herein may be used in conjunction with other types of PD machines and/or other dialysis machines or medical devices having cassettes and pumping chambers, and it is desirable for such machines and techniques to measure fluid flow therein.

The dialysate bag 122 hangs from fingers on the sides of the cart 104, and the heater bag 124 is placed in the heater tray 116. The dialysate bag 122 and the heater bag 124 are connected to the cassette 112 via a dialysate bag line 126 and a heater bag line 128, respectively. A dialysate bag line 126 can be used to transfer dialysate from the dialysate bag 122 to the cassette 112 during use, and a heater bag line 128 can be used to transfer dialysate back and forth between the cassette 112 and the heater bag 124 during use. In addition, a patient line 130 and a drain line 132 are connected to the cassette 112. The patient line 130 may be connected to the abdomen of the patient via a catheter and may be used to transfer dialysate back and forth between the cassette 112 and the peritoneal cavity of the patient during use. Prior to PD treatment, the catheter may be surgically implanted in the patient and connected to the patient line 130 via a port such as a fitting or the like. The drain line 132 may be connected to a drain system or drain container and may be used to transfer dialysate from the cartridge 112 to the drain system or drain container during use.

The PD machine 102 also includes a control unit 139 (e.g., a processor, controller, system on a chip (SoC), or the like). The control unit 139 may receive and transmit signals from and to the touch screen display 118, the control panel 120, and various other components of the PD system 100. The control unit 139 may control the operating parameters of the PD machine 102. In some embodiments, the control unit 139 includes an MPC823 PowerPC device manufactured by Motorola, Inc. The control unit 139 may also include one or more network communication components or transceivers for communicating with peripheral devices (e.g., blood pressure cuffs, weight scales, smartphones, etc.) and/or with external networks (e.g., via the internet) over short-range wireless networks, such as WiFi or bluetooth networks, and such communication may be facilitated by communication with one or more network devices, such as a gateway device located in a home with the PD machine 102.

Fig. 2 is a perspective view of the PD machine 102 and the PD cassette 112 of the PD system 100 of fig. 1, according to some embodiments. As shown in fig. 2, PD cassette 112 is placed near cassette interface 110. The cassette 112 contains

pump chambers

138A, 138B,

pressure sensing chambers

163A, 163B and valve chambers for controlling fluid flow through the chambers of the cassette 112. The cassette 112 is connected to a dialysate bag line 126, a heater bag line 128, a patient line 130, and a drain line 132.

Cartridge interface 110 includes a surface having a hole formed therein. The PD machine 102 includes

pistons

133A, 133B having piston heads 134A, 134B attached to piston shafts. The piston shaft can be actuated to move the piston heads 133A, 133B axially within

piston access ports

136A, 136B formed in the cartridge interface 110. The

pistons

133A, 133B are sometimes referred to herein as pumps. In some embodiments, the piston shaft may be connected to a stepper motor that may be operated to move the

pistons

133A, 133B axially inward and outward such that the piston heads 134A, 134B move axially inward and outward within the

piston access ports

136A, 136B. The stepper motor drives the lead screw, which causes the nut to move inward and outward on the lead screw. The stepper motor may be controlled by a drive module. The nut is in turn connected to the piston shaft, which causes the piston heads 134A, 134B to move axially inward and outward as the stepper motor drives the lead screws. The stepper motor controller provides the necessary current to drive through the windings of the stepper motor to move the

pistons

133A, 133B. The polarity of the current determines whether the

pistons

133A, 133B are advanced or retracted. In some embodiments, the stepper motor requires 200 steps for a full rotation, which corresponds to a 0.048 inch linear stroke of the piston heads 134A, 134B.

In some embodiments, the PD system 100 also includes an encoder (e.g., an optical quadrature encoder) that measures the rotational motion and direction of the lead screw. The axial position of the

pistons

133A, 133B may be determined based on the rotational movement of the lead screws, as indicated by the feedback signal from the encoder. Accordingly, the position measurements calculated based on the feedback signals may be used to track the position of the piston heads 134A, 134B of the

pistons

133A, 133B.

When the cassette 112 is positioned within the cassette compartment 114 of the PD machine 102 and the door 108 is closed, the piston heads 134A, 134B of the PD machine 102 are aligned with the

pump chambers

138A, 138B of the cassette 112 such that the piston heads 134A, 134B may be mechanically connected to the dome-shaped fastening members of the cassette 112 that cover the

pump chambers

138A, 138B. As a result of this arrangement, movement of the piston heads 134A, 134B toward the cassette 112 during treatment can reduce the volume of the

pump chambers

138A, 138B and force dialysate out of the

pump chambers

138A, 138B. Retraction of the piston heads 134A, 134B away from the cassette 112 may increase the volume of the

pump chambers

138A, 138B and cause dialysate to be drawn into the

pump chambers

138A, 138B.

The cartridge 112 also includes

pressure sensor chambers

163A, 163B. When the cassette 112 is positioned within the cassette compartment 114 of the PD machine 102 and the door 108 is closed, the

pressure sensors

151A, 151B are aligned with the

pressure sensor chambers

163A, 163B. The portions of the membrane covering the

pressure sensor chambers

163A, 163B are adhered to the

pressure sensors

151A, 151B using vacuum pressure. Specifically, the gaps around the

pressure sensors

151A, 151B communicate vacuum to the portions of the cartridge membrane that cover the

pressure sensing chambers

163A, 163B to hold those portions of the cartridge membrane tightly against the

pressure sensors

151A, 151B. The pressure of the fluid within the

pressure sensing chambers

163A, 163B causes the portions of the cartridge membrane covering the

pressure sensor chambers

163A, 163B to contact the

pressure sensors

151A, 151B and apply a force to the

pressure sensors

151A, 151B.

Pressure sensors

151A, 151B may be any sensor capable of measuring the pressure of fluid in

pressure sensor chambers

163A, 163B. In some embodiments, the pressure sensor is a solid state silicon diaphragm infusion pump force/pressure transducer. An example of such a sensor is

1865 model force/pressure transducer manufactured by Foxboro ICT. In some embodiments, the force/pressure transducer is modified to provide an increased voltage output. For example, the force/pressure transducer may be modified to produce an output signal of 0 to 5 volts.

Fig. 3 is a perspective view of the open cassette compartment 114 of the PD machine 102 of fig. 1, in accordance with some embodiments. As described above, the PD machine 102 includes

pistons

133A, 133B disposed in

piston access ports

136A, 136B, respectively. The PD machine 102 also includes a plurality of inflatable members 142 positioned within inflatable member ports 144 in the cartridge interface 110. When the cassette 112 is positioned within the cassette compartment 114 of the PD machine 102, the expandable member 142 is aligned with the depressible dome region of the cassette 112. Although only a pair of inflatable members 142 are labeled in fig. 3, it should be understood that the PD machine 102 includes an inflatable member 142 associated with each of the depressible dome regions of the cassette 112. The expandable member 142, along with the depressible dome region, acts as a valve to direct dialysate through the cassette 112 in a desired manner during use. In particular, the expandable member 142 protrudes outward beyond the surface of the cartridge interface 110 and into contact with the depressible dome region of the cartridge 112 when expanded, and retracts into the expandable member port 144 and out of contact with the cartridge 112 when contracted. Certain fluid flow paths within the cassette 112 may be occluded by inflating certain expandable members 142 to depress them at associated dome regions of the cassette 112. Thus, dialysate can be pumped through the cassette 112 by actuating the piston heads 134A, 134B, and can be directed along a desired flow path within the cassette 112 by selectively expanding and contracting the respective expandable members 142.

In some embodiments, the locating pins 148 extend from the cassette interface 110 of the PD machine 102. When the door 108 is in the open position, the cassette 112 may be loaded onto the cassette interface 110 by positioning the top portion of the cassette 112 below the locating pins 148 and pushing the bottom portion of the cassette 112 toward the cassette interface 110. The cassette 112 is sized to remain securely positioned between the detent pin 148 and a spring loaded latch 150 extending from the cassette interface 110 to allow the door 108 to close the cassette 112. The alignment pins 148 help to ensure that the proper alignment of the cassette 112 within the cassette compartment 114 is maintained during use.

The door 108 of the PD machine 102 defines

cylindrical recesses

152A, 152B that are substantially aligned with the

pistons

133A, 133B when the door 108 is in the closed position. When the cassette 112 is positioned within the cassette compartment 114 and the door 108 is closed, the

pump chambers

138A, 138B fit at least partially within the

recesses

152A, 152B. The door 108 also includes a gasket that expands during use to compress the cartridge 112 between the door 108 and the cartridge interface 110. With the cushion inflated, the portions of the door 108 forming the

recesses

152A, 152B support the surfaces of the

pump chambers

138A, 138B, and other portions of the door 108 support other areas or surfaces of the cassette 112. The door 108 may counteract the force applied by the expansion member 142, thus allowing the expansion member 142 to actuate the depressible dome region of the cartridge 112. The engagement between the door 108 and the cassette 112 may also help to maintain the cassette 112 in a desired position within the cassette compartment 114 to further ensure that the

pistons

133A, 133B are aligned with the

fluid pump chambers

138A, 138B of the cassette 112.

The control unit 139 of fig. 1 is connected to the

pressure sensors

151A, 151B, to stepper motors (e.g., drivers for the stepper motors) that drive the

pistons

133A, 133B, and to encoders that monitor the rotation of lead screws attached to the stepper motors, so that the control unit 139 can receive signals from and transmit signals to those components of the PD system 100. The control unit 139 monitors the components to which it is connected to determine whether there are any complications within the PD system 100, such as whether there is an occlusion or obstruction in the patient line 130.

Fig. 4 is an exploded perspective view of the PD cassette 112 of fig. 2 according to some embodiments. Fig. 5 is a cross-sectional view of the fully assembled PD cassette 112 of fig. 2, according to some embodiments. Fig. 6 and 7 are perspective views of the PD cassette 112 of fig. 2 from the front and back, respectively, according to some embodiments.

As shown in fig. 4-7, the PD cassette 112 includes a flexible membrane 140 attached to the periphery of a tray-like rigid base 156. Rigid dome-shaped

fastening members

161A, 161B are positioned within recessed

areas

162A, 162B of base 156. The dome-shaped

fastening members

161A, 161B are sized and shaped to receive the piston heads 134A, 134B of the PD machine 102. In some embodiments, the dome-shaped

fastening members

161A, 161B have a diameter of about 1.5 inches to about 2.5 inches (e.g., about 2.0 inches) measured from the outer edge of the

annular flanges

164A, 164B and occupy about two-thirds to about three-quarters of the area of the recessed

regions

162A, 162B. The

annular flanges

164A, 164B of the rigid dome-shaped

fastening members

161A, 161B are attached in a fluid-tight manner to portions of the inner surface of the membrane 140 surrounding the substantially

circular apertures

166A, 166B formed in the membrane 140. The

annular flanges

164A, 164B of the rigid dome-shaped

fastening members

161A, 161B may be, for example, thermally bonded or adhesively bonded to the membrane 140. The

apertures

166A, 166B of the membrane 140 expose the rigid dome-shaped

fastening members

161A, 161B such that the piston heads 134A, 134B can directly contact and mechanically connect to the dome-shaped

fastening members

161A, 161B during use.

The

annular flanges

164A, 164B of the dome-shaped

fastening members

161A, 161B form radially inwardly extending

annular projections

168A, 168B and radially outwardly extending

annular projections

176A, 176B from the sidewalls of the dome-shaped

fastening members

161A, 161B. When

piston head

134A, 134B is mechanically connected to dome-shaped

fastening member

161A, 161B, radially

inward projections

168A, 168B engage the rearward angled surfaces of sliding

latches

145A, 147A of

piston head

134A, 134B to securely fix dome-shaped

fastening member

161A, 161B to piston head 134A, 1334B. Because the membrane 140 is attached to the dome-shaped

fastening members

161A, 161B, movement of the dome-shaped

fastening members

161A, 161B into and out of the base 156 (e.g., due to the reciprocating motion of the

pistons

133A, 133B) causes the flexible membrane 140 to be similarly moved into and out of the recessed

regions

162A, 162B of the base 156. This movement allows fluid to be forced out of and drawn into the

fluid pump chambers

138A, 138B formed between the recessed

regions

162A, 162B of the base 156 and the dome-shaped

fastening members

161A, 161B and the portions of the membrane 140 that cover those recessed

regions

162A, 162B.

As shown in fig. 6, when cassette 112 is compressed between door 108 and cassette interface 110 of PD machine 102, raised ridges 167 extend from the substantially flat surface of base 156 toward and in contact with the inner surface of flexible membrane 140 to form a series of fluid pathways 158 and form a plurality of depressible dome regions 146, which depressible dome regions 146 are widened portions (e.g., substantially circular widened portions) of fluid pathways 158. The fluid passageway 158 fluidly connects a fluid line connector 160 of the cassette 112, which is an inlet/outlet port of the cassette 112, to the

fluid pump chambers

138A, 138B. As described above, the various inflatable members 142 of the PD machine 102 act on the cassette 112 during use. Dialysate flows into and out of the

pump chambers

138A, 138B through the fluid passageway 158 and the dome region 146. At each depressible dome region 146, the membrane 140 may deflect to contact a planar surface of the base 156 from which the raised ridges 167 extend. Such contact may substantially prevent (e.g., prevent) dialysate from flowing along the region of the pathway 158 associated with the dome region 146. Thus, by selectively inflating the inflatable member 142 of the PD machine 102, the depressible dome region 146 can be selectively depressed to control the flow of dialysate through the cassette 112.

The fluid line connector 160 is located along the bottom edge of the cassette 112. As described above, the fluid path 158 in the cassette 112 leads from the

pumping chambers

138A, 138B to the various connectors 160. The connectors 160 are asymmetrically positioned along the width of the cassette 112. The asymmetric positioning of the connector 160 helps ensure that the cartridge 112 will be properly positioned in the cartridge compartment 114 with the membrane 140 of the cartridge 112 facing the cartridge interface 110. The connector 160 is configured to be able to receive fittings on the ends of the dialysate bag line 126, the heater bag line 128, the patient line 130, and the drain line 132. One end of the fitting may be inserted into and coupled to its respective line, while the other end may be inserted into and coupled to its associated connector 160. By allowing the dialysate bag line 126, the heater bag line 128, the patient line 130, and the drain line 132 to connect to the cassette 112, as shown in fig. 1 and 2, the connector 160 allows dialysate to flow into and out of the cassette 112 during use. As

pistons

133A, 133B reciprocate, expandable member 142 may be selectively expanded to allow fluid to flow from any of

lines

126, 128, 130, and 132 to any of

ports

185A, 185B, 187A, and 187B of

pump chambers

138A, 138B or to allow fluid to flow from any of

ports

185A, 185B, 187A, and 187B of

pump chambers

138A, 138B to any of

lines

126, 128, 130, and 132.

The rigidity of the base 156 helps to hold the cassette 112 in place within the cassette compartment 114 of the PD machine 102 and prevents the base 156 from bending and deforming in response to forces applied to the

projections

154A, 154B by the dome-shaped

fastening members

161A, 161B and in response to forces applied to the planar surface of the base 156 by the expandable member 142. The dome-shaped

fastening members

161A, 161B are also sufficiently rigid that they do not deform due to the normal pressures that occur in the

pump chambers

138A, 138B during the fluid pumping process. Thus, in addition to the movement of the

pistons

133A, 133B, the deformation or bulging of the annular portions 149A, 149B of the membrane 140 can be considered the only factor that affects the volume of the

pump chambers

138A, 138B during the pumping process.

The base 156 and dome-shaped

fastening members

161A, 161B of the cassette 112 may be formed from any of a variety of relatively rigid materials. In some embodiments, these components of cassette 112 are formed from one or more polymers, such as polypropylene, polyvinyl chloride, polycarbonate, polysulfone, and other medical grade plastic materials. In some embodiments, these components may be formed from one or more metals or alloys, such as stainless steel. These components may alternatively be formed from various different combinations of the above-described polymers and/or metals/alloys. These components of the cassette 112 may be formed using any of a variety of different techniques, including machining, molding, and casting techniques.

As described above, the membrane 140 is attached to the baseThe periphery of the seat 156 and the

annular flanges

164A, 164B of the dome-shaped

fastening members

161A, 161B. The portion of the membrane 140 covering the remainder of the base 156 is typically not attached to the base 156. Instead, these portions of the membrane 140 lie loosely on top of the raised ridges 165A, 165B, and 167 extending from the planar surface of the base 156. Any of a variety of attachment techniques, such as adhesive bonding and thermal bonding, may be used to attach the membrane 140 to the periphery of the base 156 and the dome-shaped

fastening members

161A, 161B. The thickness and material of the membrane 140 are selected such that the membrane 140 has sufficient flexibility to flex toward the base 156 in response to a force applied to the membrane 140 by the inflatable member 142. In some embodiments, the thickness of the membrane 140 is about 0.100 microns to about 0.150 microns. However, various other thicknesses may be sufficient depending on the type of material used to form the membrane 140. Any of a variety of different materials that allow the membrane 140 to deflect without tearing in response to movement of the inflatable member 142 may be used to form the membrane 140. In some embodiments, film 140 comprises a trilaminate. In some embodiments, the laminate has an inner and outer layer of 60% pass through

8004 thermoplastic rubber (i.e., hydrogenated styrenic block copolymer) and 40% ethylene, the middle layer is formed by a mixture of 25% ethylene

H1062 (SEBS: hydrogenated styrene thermoplastic elastomer), 40%

8003 polyolefin elastomer (ethylene octane copolymer) and 35% of

8004 thermoplastic rubber (i.e., hydrogenated styrenic block copolymer). The membrane 140 may alternatively include more or fewer layers and/or may be formed of different materials.

Fig. 8 illustrates a PD cassette 112 resting on a cassette interface 110 according to some embodiments. As shown in fig. 8, prior to beginning PD therapy, the door 108 of the PD machine 102 is opened to expose the cassette interface 110, and the cassette 112 is positioned with dome-shaped

fastening members

161A, 161B aligned with the

pistons

133A, 133B of the PD machine 102,

pressure sensing chambers

163A, 163B aligned with the

pressure sensors

151A, 151B of the PD machine 102, a depressible dome region 146 aligned with the inflatable member 142 of the PD machine 102, and a membrane 140 adjacent the cassette interface 110. To ensure that cassette 112 is properly positioned on cassette interface 110, cassette 112 is positioned between locating pins 148 and spring loaded latches 150 extending from cassette interface 110. The asymmetrically positioned connectors 160 of the cartridge 112 serve as a key feature that reduces the likelihood that the cartridge 112 will be installed as a film 140 and the dome-shaped

fastening members

161A, 161B facing in the wrong direction (e.g., outwardly toward the door 108). Additionally or alternatively, the detent pin 148 may be sized to be less than the maximum protrusion of the

protrusions

154A, 154B, such that the cassette 112 cannot contact the detent pin 148 if the membrane 140 is facing outward toward the door 108. During installation of the cartridge 112, the

pistons

133A, 136B will typically retract into the

piston access ports

136A, 136B to avoid interference between the

pistons

133A, 133B and the dome-shaped

fastening members

161A, 161B, thus increasing the ease with which the cartridge 112 can be positioned within the cartridge compartment 114.

After the cassette 112 is positioned on the cassette interface 110 as desired, the door 108 is closed and the inflatable cushion within the door 108 is inflated to compress the cassette 112 between the inflatable cushion and the cassette interface 110. Compression of cassette 112 retains

tabs

154A, 154B of cassette 112 in

recesses

152A, 152B of door 108 and tightly presses membrane 140 against raised ridge 167 extending from the planar surface of rigid base 156 to form enclosed fluid pathway 158 and dome region 146. The patient line 130 is then connected to the abdomen of the patient via a catheter, and the drain line 132 is connected to a drain system or drain container. In addition, a heater bag line 128 is connected to the heater bag 124 and a dialysate bag line 126 is connected to the dialysate bag 122. At this time, the

pistons

133A, 133B may be coupled to the dome-shaped

fastening members

161A, 161B of the cassette 112 to allow perfusion of the cassette 112 and one or more of the

lines

126, 128, 130, and 132. Once these components have been primed, PD therapy can begin.

Fig. 9A-9G are cross-sectional views of PD system 100 at various stages of setup, perfusion, and treatment, according to some embodiments. The portion of the PD system 100 shown in fig. 9A-9G focuses on the interaction of the piston 133A of the PD machine 102 with the pumping chamber 138A of the cassette 112 during setup, priming, and treatment. The interaction between the other piston 133B and the other pump chamber 138B is similar to that shown in fig. 9A-9G and, therefore, will not be separately described herein to avoid repetition.

As shown in fig. 9A, the piston 133A is fully retracted into the piston access port 136A of the cartridge interface 110. The cassette 112 is positioned in the cassette compartment 114 of the PD machine 102 and the inflatable gasket in the door 108 of the PD machine 102 is inflated so that the cassette 112 is tightly pressed against the cassette interface 110 of the PD machine 102.

With the cassette 112 properly installed in the cassette compartment 114 of the PD machine 102 and the appropriate line connections made, the piston 133A is advanced to begin mechanically connecting the piston head 134A of the PD machine 102 to the dome-shaped fastening member 161A of the cassette 112, as shown in fig. 9B. As the piston 133A advances, the forward angled surface 188A of the sliding latch 145A and the forward angled surface 191A of the sliding latch 147A contact the rear surface of the annular protrusion 168A, which extends radially inward from the dome-shaped fastening member 161A. The rear surface of the annular projection 168A is substantially perpendicular to the longitudinal axis of the piston 133A.

As the piston 133A continues to advance, the dome-shaped fastening member 161A contacts the inner surface of the portion of the rigid base 156 that forms the recessed area 162A. The rigid base 156 prevents further forward movement of the dome-shaped fastening member 161A. The membrane 140 attached to the peripheral flange 164A of the dome-shaped fastening member 161A is also stretched and moved into the recessed area 162A by the advancing piston 133A. Due to the angled geometry of the forward

angled surfaces

188A, 191A of the sliding

latches

145A, 147A and the resistance provided by the rigid base 156 to forward movement of the dome-shaped fastening member 161A, the sliding

latches

145A, 147A are caused to move radially inward (e.g., toward the longitudinal axis of the piston 133A) as the piston head 134A continues to advance relative to the dome-shaped fastening member 161A. More specifically, the forward movement of the sliding

latches

145A, 147A is converted to a combined forward and radially inward movement due to the sliding movement of the forward

angled surfaces

188A, 191A of the sliding

latches

145A, 147A against the rear surface of the annular protrusion 168A of the dome-shaped fastening member 161A. The radially inward movement of each of the sliding

latches

145A, 147A in turn causes the latches 141A of the piston head 134A to move forward due to the matching geometry of the outer surfaces of the

legs

155A, 157A of the latches 141A and the surfaces of the sliding

latches

145A, 147A adjacent to and in contact with those outer surfaces of the

legs

155A, 157A. This forward movement of latch 141A is prevented by spring 143A disposed in a recessed portion of piston head 134A.

As shown in fig. 9C, piston head 134A is at a point during the connection process where sliding latches 145A, 147A have deflected radially inward a sufficient distance to allow sliding

latches

145A, 147A to clear annular protrusion 168A extending radially inward from dome-shaped fastening member 161A. In this position, the peripheral surfaces of the sliding

latches

145A, 147A that are substantially parallel to the longitudinal axis of the piston 133A contact and slide along the inner surface of the annular protrusion 168A of the dome-shaped fastening member 161A that is also substantially parallel to the longitudinal axis of the piston 133A. Due to the deflected position of the sliding

latches

145A, 147A, the spring 143A is further compressed.

As shown in fig. 9D, the spring 143A is allowed to expand as the sliding

latches

145A, 147A pass over the annular projection 168A. The expansion of the spring 143A causes the latch 141A to move rearward. Accordingly, the outer surfaces of the

legs

155A, 157A of the latch 141A contact the respective angled adjacent surfaces of the sliding

latches

145A, 147A, thereby moving the sliding

latches

145A, 147A radially outward under the annular protrusion 168A of the dome-shaped fastening member 161A. As the sliding

latches

145A, 147A move radially outward, rearward angled

surfaces

190A, 193A of the sliding

latches

145A, 147A extend along a front surface of an annular projection 168A of the dome-shaped fastening member 161A that is slightly angled toward the rear of the dome-shaped fastening member 161A. As the sliding

latches

145A, 147A move radially outward, the sliding

latches

145A, 147A become wedged under the annular protrusion 168A.

As shown in fig. 9E, the piston head 134A and the dome-shaped fastening member 161A are mechanically engaged by a mechanism in which the sliding

latches

145A, 147A have moved to a maximum outwardly displaced position on the inside of the annular protrusion 168A within the dome-shaped fastening member 161A. In this configuration, the annular protrusion 168A of the dome-shaped fastening member 161A is effectively sandwiched between the rear member 137A of the piston head 134A and the rearward

angled surfaces

190A, 193A of the sliding

latches

145A, 147A, thereby creating a secure mechanical connection between the piston head 134A and the dome-shaped fastening member 161A. Due to the mechanical engagement of piston head 134A with dome-shaped fastening member 161A, the amount of sliding of piston head 134A relative to dome-shaped fastening member 161A may be reduced (e.g., minimized), such that accurate pumping may be achieved.

After mechanically coupling the piston head 134A of the PD machine 102 to the dome-shaped fastening member 161A of the cassette 112, a priming procedure is performed to remove air from the cassette 112 and the

various lines

126, 128, 130, and/or 132 connected to the cassette 112. To prime the cassette 112 and

lines

126, 128, 130, 132, the piston 133A and expandable member 142 are typically operated to pump dialysate from the heater bag 124 to the drain system and from each of the dialysate bags 122 to the drain system. Dialysate is also passed (e.g., by gravity) from the heater bag 124 to the patient line 130 to force any air trapped in the patient line out of a hydrophobic filter positioned at the distal end of the patient line 130.

As shown in fig. 9F, after the priming procedure is completed, the patient line 130 is connected to the patient and the PD machine 102 is operated to drain any spent dialysate left in the peritoneal cavity of the patient from the previous treatment. To drain the spent dialysate from the peritoneal cavity of the patient, the expandable member 142 of the PD machine 102 is configured to create an open fluid flow path between the patient line 130 and a port 187A (shown in fig. 4) fluidly coupled to the pump chamber 138A, and the piston 133A is retracted to draw spent dialysate from the peritoneal cavity of the patient into the pump chamber 138A via the patient line 130. Since the piston head 134A is mechanically connected to the dome-shaped fastening member 161A, and the dome-shaped fastening member 161A is attached to the membrane 140 of the cassette 112, retraction of the piston 133A causes the dome-shaped fastening member 161A and the portion of the membrane 140 attached to the dome-shaped fastening member 161A to move rearward, away from the rigid base 156. As a result, the volume of the pump chamber 138A increases, decreasing the pressure of the fluid contained therein, and used dialysate is drawn into the pump chamber 138A from the patient's peritoneal cavity due to the pressure differential across the distal end of the patient line 130. Spent dialysate travels from the patient line 130 through the pressure sensing chamber 163A of the cassette 112 and then into the pump chamber 138A via port 187A. During this process, pressure sensor 151A monitors the fluid pressure in pressure sensing chamber 163A, which is approximately equal to the fluid pressure in pump chamber 138A.

As shown in fig. 9G, after drawing dialysate from the peritoneal cavity of the patient into the pump chamber 138A, the expandable member 142 of the PD machine 102 is configured to create an open fluid flow path between the port 185A (shown in fig. 4) fluidly coupled to the pump chamber 138A and the drain line 132, and the piston 133A is advanced to force dialysate from the pump chamber 138A to the drain system or drain container. The piston 133A is typically advanced until the dome-shaped fastening member 161A contacts or nearly contacts the inner surface of the recessed region 162A of the base 156, such that substantially all of the dialysate is forced out of the fluid pump chamber 138A via the port 185A.

During a patient drain phase of treatment, the

pistons

133A, 133B typically alternate operation such that the piston 133A is retracted to draw spent dialysate solution from the patient into the pump chamber 138A while the piston 133B is advanced to pump spent dialysate solution from the pump chamber 138B to a drain system or drain container, and vice versa.

To begin the patient fill phase, the expandable member 142 is configured to create an open fluid flow path between the pump chamber 138A and the heater bag line 128, and then the piston 133A is retracted, as shown in fig. 9F, to draw warm dialysate from the heater bag 124 into the pump chamber 138A. Warm dialysate travels from the heater bag 124 through the heater bag line 128 and into the pump chamber via port 185A.

Then, by configuring the expandable member 142 to create an open fluid flow path between the pump chamber 138A and the patient line 130, and then delivering warm dialysate to the peritoneal cavity of the patient via the patient line 130, the piston 133A is advanced to pump the warm dialysate to the patient, as shown in fig. 9G. Warm dialysate exits the pump chamber 138A via port 187A and travels through the pressure sensing chamber 163A to the patient line 130 before reaching the patient's peritoneal cavity. During this process, pressure sensor 151A monitors the fluid pressure in pressure sensing chamber 163A, which is approximately equal to the fluid pressure in pump chamber 138A.

During the patient fill phase of treatment, the

pistons

133A, 133B typically alternate operation such that the piston 133A is retracted to draw warm dialysate from the heater bag 124 into the pump chamber 138A while the piston 133B is advanced to deliver warm dialysate from the pump chamber 138B to the patient, and vice versa. When the desired volume of dialysate has been pumped to the patient, the machine 102 transitions from the patient fill phase to the dwell phase. During the dwell phase, the dialysate is allowed to dwell in the patient's peritoneal cavity for a long period of time.

During the dwell period (e.g., a period of time referred to as the dwell period), toxins pass from the patient's blood into the dialysate through the patient's peritoneum. While the dialysate remains in the patient, the PD machine 102 prepares fresh dialysate for delivery to the patient in a subsequent cycle. In particular, the PD machine 102 pumps fresh dialysate from one of the four filled dialysate bags 122 into the heater bag 124 for heating. To this end, the pump of the PD machine 102 is activated to reciprocate the

pistons

133A, 133B and certain expandable members 142 of the PD machine 102 are expanded to draw dialysate from a selected dialysate bag 122 into the

fluid pump chambers

138A, 138B of the cassette 112 via its associated line 126. The dialysate is then pumped from the

fluid pump chambers

138A, 138B to the heater bag 124 via the heater bag line 128.

After the dialysate has been resident in the patient for a desired period of time, the spent dialysate is pumped from the patient to the drain line 132 in the manner described above. The heated dialysate is then pumped from the heater bag 124 to the patient where it is held for a desired period of time. These steps are repeated with dialysate from two of the three remaining dialysate bags 122. The dialysate from the last dialysate bag 122 is typically delivered to the patient and remains with the patient until a subsequent PD treatment.

After the PD treatment is completed, the

pistons

133A, 133B are retracted in a manner that disconnects the piston heads 134A, 134B from the dome-shaped

fastening members

161A, 161B of the cassette. Then, the door 108 of the PD machine 102 is opened, and the cassette 112 is removed from the cassette compartment 114 and discarded.

Fig. 10 illustrates a path between a patient and the PD machine 102 when the patient is receiving PD therapy, according to some embodiments. As shown in fig. 10, the proximal end of the patient line 130 is connected to the cassette 112 installed in the PD machine 102. The distal end of the patient line 130 is connected to the abdomen 1006 of the patient via a catheter 1002. Conduit 1002 is connected to a patient line via port 1004. In some embodiments, the patient line 130 may be a hollow tube formed of an expandable and/or flexible material that expands at least partially due to operating pressures in the PD machine 102. In other words, the fluid pressure radially expands the outer wall of the hollow tube, thereby enabling fluid flow through the center of the tube. For example, in some embodiments, the patient line 130 may be made of an elastomeric material, such as a polymer, that expands in response to positive operating pressures in the fluid caused by the pumping action of the PD machine 102. The patient line 130, port 1004, and conduit 1002 are sometimes referred to as patient line-conduit tubing, or simply tubing.

It should be appreciated that, during use, at least one of the

pump chambers

138A, 138B and the

pressure sensing chambers

163A, 163B of the cassette 112 are fluidly coupled to the proximal end of the patient line 130 so as to cause fluid (e.g., dialysis solution) to flow through the patient line 130 in response to movement of the

pistons

133A, 133B.

Pressure sensors

151A, 151B may continuously monitor the fluid pressure in respective

pressure sensing chambers

163A, 163B. The signals generated by the

pressure sensors

151A, 151B are indicative of the magnitude and direction of fluid flow into or out of the

pump chambers

138A, 138B, and, due to the particular configuration of the expandable member 142, can indicate the flow of fluid through the patient line 130, drain line 132, dialysate bag line 126, or heater bag line 128 (connected to the heater bag 124).

As shown in fig. 10, the proximal end of the drain line 132 is connected to the cassette 112, and the distal end of the drain line 132 is connected to a drain system 1010 or a drain container such as a bag, bucket, or other container capable of holding a fluid. In some embodiments, the drain line 132 may be a hollow tube formed of an expandable and/or flexible material that is expanded at least partially by the operating pressure in the PD machine 102. In some embodiments, the drain line 132 may be made of an elastomeric material, such as a polymer, that expands in response to positive operating pressures in the fluid caused by the pumping action of the PD machine 102. It should be appreciated that the distal end of the exhaust line 132 may be open to air to facilitate discharge of fluid to the exhaust system 1010. In some embodiments, drain line 132 may include a one-way valve, such as a check valve, that prevents fluid from flowing back from drain system 1010 to cassette 112. The one-way valve may also prevent air in the exhaust line from being introduced into the cassette 112, which may reduce the reliability of the readings of the

pressure sensors

151A, 151B.

Fig. 11A-11F illustrate a fluid flow path from heater bag line 128 to patient line 130 through cassette 112 according to some embodiments. As shown in fig. 11A, the cassette 112 includes

pump chambers

138A, 138B,

pressure sensing chambers

163A, 163B, and a plurality of valve chambers 1110. The valve chamber 1110 controls the flow of fluid through the cavity of the cartridge 112.

During normal operation, fluid (e.g., dialysate) is pumped from the heater bag line 128 to the patient line 130 using an alternating flow path through the first or

second pump chambers

138A, 138B. The configuration of the valve chamber 1110 during each stroke of the

pistons

133A, 133B determines whether a particular volume of fluid is pumped into the first or

second pump chamber

138A, 138B and whether the particular volume of fluid is not pumped into the other pump chamber before being expelled into the patient line 130. While the

pressure sensing chambers

163A, 163B and

pistons

133A, 133B may be used to measure or estimate the volume of fluid in the

pump chambers

138A, 138B during operation, for example, to detect problems such as possible line occlusions, leaks in the line, rupture of the cassette 112, and the like, the total amount of fluid passing through the cassette 112 is typically not accumulated based on these measurements.

In some embodiments, the fluid flow path through the cassette 112 may be modified in order to improve the accuracy of the measurement of the total fluid volume passing through the cassette 112 during operation of the PD cycler. Multiple measurements for each particular volume of fluid may be measured in multiple different pumping chambers of the cassette 112. For example, as shown in the cassette 112 of FIG. 11A, measurements of fluid volumes may be taken in the first pumping chamber 138A and the second pumping chamber 138B. The various measurements may be compared and, in some embodiments, an estimate of the fluid volume for a particular volume of fluid may be calculated. In some embodiments, the estimate of the fluid volume is an average of the individual measurements. Further, in some embodiments, a range of measurement values may be calculated and if the range is greater than a threshold, an alarm may be set that may indicate a potential problem with the PD cycler. It should be understood that the volumes of the

pump chambers

138A, 138B should be the same, although in practice the volumes may not be exactly the same due to unit-to-unit variations in manufacturing. After fluid has been pumped from the first pumping chamber 138A to the second pumping chamber 138B, the fluid volume measurement of the fluid in the first pumping chamber 138A should be the same as (or substantially similar to) the second fluid volume measurement in the second pumping chamber 138B. If the first measurement differs significantly from the second measurement, the difference may be an indication of a problem such as a pressure sensor failure, a piston breakage, a blockage or manufacturing defect in the cassette 112, a leak in the cassette 112, or the like.

As shown in fig. 11B, during the first time period, the PD cycler operates the first piston 133A connected to the dome-shaped fastening member 161A to draw fluid into the first pump chamber 138A. As the piston 133A retracts into the PD cycler, the pressure in the first pump chamber 138A drops (due to the increased volume of the first pump chamber 138A), drawing fluid from the heater bag line 128 into the first pump chamber 138A (and all cavities and valve chambers 1110 in the fluid flow path therebetween). The fluid is shown in a fill pattern within the cavity of the cartridge 112, the valve chamber 1110, the first pressure chamber 163A, or the first pump chamber 138A. The valve chamber 1110 shown by an X enclosed within a circle indicates that the valve chamber 1110 is closed (e.g., fluid cannot pass through the valve chamber 1110), wherein the valve chamber 1110 shown by a fill pattern indicates that the valve chamber 1110 is open (e.g., fluid can pass through the valve chamber 1110). The valve chamber 1110, shown empty, is in a closed or open state, depending on the additional fluid path formed in the cartridge 112 during the first time period consistent with other parallel operations. For example, it should be understood that the configuration of the valve chamber 1110 shown in fig. 11B may allow for pumping fluid out of the second pump chamber 138B while pumping fluid into the first pump chamber 138A.

During the second time period, the PD cycler closes the valve chambers 1110-1 and 1110-2 to trap a volume of fluid in the first pump chamber 138A and the first pressure chamber 163A and the cavity connected thereto, as shown in FIG. 11C. The piston 133A extends from the PD cycler, reducing the volume in the first pump chamber 138A. Monitoring the pressure signal from the pressure sensor in contact with first pressure chamber 163A, controller 139 may determine when the position of piston head 134A corresponds to the volume of fluid in first pump chamber 138A based on the pressure rise detected by the pressure sensor. In other words, due to the incompressible nature of the fluid, at the point where any air in the first pump chamber 138A has been compressed and the piston 133A acts primarily on the fluid, the pressure rises significantly due to the operation of the piston 133A. At this point, the volume of fluid in first pump chamber 138A matches well the volume of cassette 112 between first valve chamber 1110-1 and second valve chamber 1110-2, including the volume of first pump chamber 138A and first pressure chamber 163A plus the cavity to which they are connected, and the measured position of piston head 134A provides an accurate first fluid volume measurement.

Given the cell-to-cell variation (e.g., manufacturing tolerances, defects, etc.) of different cartridges 112, the measurements taken by the control unit 139 are associated with a particular accuracy that may not be known. However, by making independent measurements on the same data point, the accuracy of the measurement can be improved. Assuming that the nominal volume of first pump chamber 138A is the same as the nominal volume of second pump chamber 138B, and the nominal volume of first pressure chamber 163A is the same as the nominal volume of second pressure chamber 163B, a second independent measurement of the same volume of fluid may be taken by transferring fluid from first pump chamber 138A to second pump chamber 138B and taking another independent measurement.

As shown in fig. 11D, during the third time period, the PD cycler closes the valve chamber to form a fluid flow path between the first pumping chamber 138A and the second pumping chamber 138B. The valve chamber 1110 is opened to facilitate fluid flow between the first and

second pump chambers

138A, 138B. Fluid is forced out of the first pumping chamber 138A by a first piston 133A extending from the PD cycler, and into the second pumping chamber 138B by a second piston 133B retracting into the PD cycler.

During a fourth time period, the PD cycler closes the valve chambers 1110-3 and 1110-4 to capture the fluid volumes in the second pump chamber 138B and the second pressure chamber 163B and the cavity connected thereto, as shown in FIG. 11E. The piston 133B extends from the PD cycler, reducing the volume in the second pump chamber 138B. Similar to the discussion above with reference to fig. 11C, monitoring the pressure signal from the pressure sensor in contact with second pressure chamber 163B, controller 139 can determine when the position of piston 133B is indicative of the volume of fluid in second pump chamber 138B. In other words, given the measured position of the piston head 134B, when the volume of the cassette 112 between the third and fourth valve chambers 1110-3 and 1110-4 decreases due to operation of the piston 133B, the volume of the cassette 112 between the third and fourth valve chambers 1110-3 and 1110-4, including the volume of the second and

second pump chambers

138B and 163B plus the cavity connected thereto, can be estimated based on the pressure rise due to the incompressible nature of the fluid.

The second measurement provides a second estimate of the same volume of fluid that should have passed through and been measured in the first pumping chamber 138A. Thus, the second measurement provides a second data point of the same property of the fluid. It should be appreciated that the volume of the first pump chamber 138A may not equal the volume of the second pump chamber 138B due to variations in the cassette 112. Thus, by performing a statistical analysis on the individual data points, the actual volume of the fluid can be better estimated.

In one embodiment, the control unit 139 estimates the volume of the fluid by calculating an average (e.g., mean) of a plurality of independent measurements made in different pumping chambers 138 of the cassette 112. It should be understood that the PD cycler shown herein uses two pistons and two pump chambers. However, the description is not so limited, and various embodiments of different PD cyclers may incorporate additional pump chambers/pistons to allow for more than two independent measurements. For example, the techniques described above may be extended to cassettes having three or more pump chambers and PD cyclers having three or more pistons configured to be operable as pumps. In such a system, three or more independent measurements may be combined (e.g., by taking the average of all independent values) to estimate the fluid flow volume through the PD cycler.

As shown in fig. 11F, during the fifth time period, fluid in the second pumping chamber 138B is forced from the second pumping chamber 138B into the patient line 130 via the configuration of the valve chamber as shown. It should be appreciated that as the piston 133B forces fluid from the second pumping chamber 138B into the patient line 130, the other piston 133A may draw fluid from the heater bag line 128 into the first pumping chamber 138A to take a first measurement of a second volume of fluid. Over the multiple cycles shown in fig. 11B-11F, the total volume of fluid passing through the cassette 112 can be tracked by accumulating an estimate of each discrete volume of fluid passing through the multiple pump chambers 138. The PD cycler can then use this estimated total volume to determine when a given dialysate bag (e.g., heater bag 124) is likely to be nearly empty. In some embodiments, the control unit 139 may utilize the estimated total volume to begin a refill cycle in which dialysate is pumped from the second dialysate bag into the heater bag 124.

The reverse process may be used to monitor the flow of fluid into the heater bag line 128 from one of the other line connections to the cassette 112. More specifically, during the refill cycle, fluid from the second dialysate bag pumped to the heater bag 124 can be measured and the fluid volume can be accumulated into an estimated total volume. For example, incremental volume measurements per pump cycle may be added to the estimated total volume to monitor the amount of dialysate in the heater bag 124 as fluid is added to the heater bag 124.

Fig. 12 is a flow diagram of a method 1200 for measuring fluid flow in a peritoneal dialysis machine according to some embodiments. It should be understood that method 1200 is described as being performed by PD system 100. More specifically, the various steps described below may be implemented by a processor such as the control unit 139 of the PD machine 102 configured to be able to execute a number of instructions. However, it should be understood that method 1200 may be performed by any PD machine configured to drain fluid from the peritoneal cavity of a patient during a PD cycle. In various embodiments, the method 1200 may be implemented using hardware, software executed by a general purpose processor configured to be capable of controlling a special purpose device such as a PD machine, or a combination of hardware and software.

At step 1202, a fluid, such as dialysate, is drawn into the first pump chamber 138A that is fluidly connected to the first pressure chamber 163A. In some embodiments, the cassette 112 is loaded into the PD machine 102. The first piston 133A engages the first pump chamber 138A. In one embodiment, the piston head 134A engages a dome-shaped fastening member 161A that allows the piston 133A to change the volume of the first pump chamber 138A. Retraction of the first piston 133A into the PD machine 102 increases the volume of the first pump chamber 138A and draws fluid from the connected heater bag line 128 through the fluid path in the cassette 112.

In step 1204, the pressure in the first pressure chamber 163A is monitored by the control unit 139. In one embodiment, after the first piston 133A is fully retracted such that fluid has been drawn into the first pump chamber 138A, the first set of valve chambers 1110 is closed to confine a portion of the fluid in the first portion of the cartridge 112. The first portion of the cassette 112 includes a first pump chamber 138A fluidly connected to a first pressure chamber 163A. Piston 133A extends from PD machine 102 to reduce the volume of first pump chamber 138A while control unit 139 monitors the pressure signal from a pressure transducer configured to measure the fluid pressure in first pressure chamber 163A. The first piston 133A extends to reduce the volume of the first pump chamber 138A, thereby compressing the air and fluid trapped therein. When air is compressed, the pressure signal may rise slightly due to the compressible nature of the air. However, at the point where the air has been significantly compressed and the extended position of the first piston 133A has reduced the volume of the first pump chamber 138A such that the volume of the fluid is substantially equal to the volume of the first portion of the cassette 112, the pressure signal will experience a significant change in slope and a rapid rise due to the incompressible nature of the fluid as compared to air. Thus, such a change in the pressure signal may be used to trigger a measurement of the volume of the first fluid captured in the first portion of the cartridge 112.

At step 1206, a first fluid volume in a first portion of the cartridge 112 is measured. The measurement may be triggered by a change in the pressure signal in step 1204. When the control unit 139 detects a change in the pressure signal, the control unit 139 measures the first fluid volume based on the current position of the piston 133A. It will be appreciated that the position of the piston 133A is indicative of the volume of the first pump chamber 138A and the first portion of the cassette 112. In one embodiment, the position of the piston 133A is given, for example, by an optical encoder signal coupled to a lead screw that actuates the piston 133A. In other embodiments, the position may be sensed using other technically feasible techniques, such as inferring the position of the stepper motor by counting steps of the stepper motor or using other feedback signals from other types of sensors.

At step 1208, fluid is transferred from the first pump chamber 138A to the second pump chamber 138B, which is fluidly connected to the second pressure chamber 163B. In some embodiments, the valve chamber 1110 is configured to form a fluid path in the cassette 112 that connects the first pump chamber 138A to the second pump chamber 138B. The first piston 133A extends and the second piston 133B retracts to move fluid from the first pumping chamber 138A to the second pumping chamber 138B.

At step 1210, the pressure in the second pressure chamber 163B is monitored by the control unit 139. Similar to step 1204 of the first pressure chamber 163A, after the second piston 133B is fully retracted so that fluid has been drawn into the second pump chamber 138B, the second set of valve chambers 1110 is closed to confine fluid in the second portion of the cartridge 112. A second portion of the cassette 112 includes a second pump chamber 138B fluidly connected to a second pressure chamber 163B. Piston 133B extends from PD machine 102 to reduce the volume of second pump chamber 138B while control unit 139 monitors the pressure signal from a pressure sensor configured to measure the fluid pressure in second pressure chamber 163B. The second piston 133B is extended to reduce the volume of the second pump chamber 138B, thereby compressing the air and fluid trapped therein. When air is compressed, the pressure signal may rise slightly due to the compressible nature of the air. However, at the point where the air has been significantly compressed and the extended position of the second piston 133B has reduced the volume of the second pump chamber 138B such that the volume of the fluid is substantially equal to the volume of the second portion of the cassette 112, the pressure signal will experience a significant change in slope and a rapid rise due to the incompressible nature of the fluid as compared to air. Thus, such a change in the pressure signal may be used to trigger a measurement of the volume of the second fluid trapped in the second portion of the cartridge 112.

At step 1212, a second volume of fluid in a second portion of the cartridge 112 is measured. The measurement may be triggered by a change in the pressure signal in step 1210. When the control unit 139 detects a change in the pressure signal, the control unit 139 measures a second fluid volume based on the current position of the piston 133B. It should be appreciated that the position of the piston 133B is indicative of the volume of the second pump chamber 138A and the second portion of the cassette 112. In one embodiment, the position of the piston 133B is given by an optical encoder signal coupled to a lead screw that actuates the piston 133B. In other embodiments, other technically feasible techniques may be used to sense position.

At step 1214, the measured fluid volume for the single pump cycle is determined by the control unit 139 based on the first fluid volume and the second fluid volume. In one embodiment, the average of the fluid volumes measured in each portion of the cartridge 112 is calculated as the measured fluid volume. In other embodiments, a minimum or maximum fluid volume may be selected as the measured fluid volume.

Although the method 1200 is based on a cassette 112 having two different pumping chambers 138, in other embodiments, the method 1200 can be extended to cassettes 112 having three or more pumping chambers by repeating steps 1208 to 1212 for each additional pumping chamber, and then determining the measured fluid volume based on all of the individual measurements for each of the three or more pumping chambers.

It should be understood that the terms "less than" or "greater than" as used above may include "less than or equal to" or "greater than or equal to," respectively, and that determining whether to compare inclusion or exclusion thresholds is merely a design choice, unless the context clearly contradicts otherwise.

Fig. 13 is a flow diagram of a method 1300 for determining a measured fluid volume and/or setting an alarm, according to some embodiments. In one embodiment, a portion of method 1300 may be performed as step 1210 of method 1200 described above.

In step 1302, a difference between the first fluid volume and the second fluid volume is calculated. The difference may indicate a difference between the two measurements, which may have various causes. For example, the manufacturing variation may be such that there is a difference between the volume of a first portion of the cartridge 112 and a second portion of the cartridge 112. Other causes may include defects in the cassette 112, such as leaks or blockages in the cavity between the first and

second pump chambers

138A, 138B, or deviations in the pressure sensor signal calibration.

At step 1304, the difference is compared to a threshold. In one embodiment, the absolute value of the difference is compared to a threshold value, such that the difference is always positive and reflects the magnitude of the difference between the first fluid volume and the second fluid volume. In some embodiments, the threshold value is a fixed value that is a percentage of the maximum nominal volume of the pump chamber. In other embodiments, the threshold is dynamically set based on a percentage of the first fluid volume. For example, the threshold may be set to 10% of the first fluid volume such that the comparison indicates whether the second fluid volume differs from the first fluid volume by more than 10% of the initial measurement.

If the difference is less than the threshold, then at step 1306, a measured fluid volume is calculated based on the first fluid volume and the second fluid volume. In one embodiment, the measured fluid volume is calculated by taking the average of the first fluid volume and the second fluid volume. In another embodiment, the measured fluid volume is calculated by taking the minimum of the first fluid volume or the second fluid volume. In yet another embodiment, the measured fluid volume is calculated by taking the maximum of the first fluid volume or the second fluid volume.

Returning to step 1304, if the difference is greater than the threshold, then at step 1308, an alarm is set. Likewise, a large difference in the two independent measurements may indicate a possible problem with the cassette 112, fluid line, or PD machine 102. In one embodiment, the alarm may trigger the PD machine to take remedial action such as pausing PD therapy and causing a message to be displayed on the touch screen display 118 of the PD machine 102 at step 1310. The administrator or patient may clear the alarm to continue PD therapy.

It should be appreciated that the method 1200 calculates a measured fluid volume for a single pump cycle of the PD machine 102. In some embodiments, the measured fluid volume may be accumulated in a total fluid volume variable to monitor the total fluid volume drawn from the heater bag line 128. If the control unit 139 determines that the total amount of fluid drawn from the heater bag line is above the threshold, the control unit 139 can configure the cassette 112 to draw fluid from the second dialysis bag line 126 to transfer additional fluid to the heater bag line 128. In some embodiments, the control unit 139 is configured to be able to measure the amount of fluid transferred to the heater bag line 128 and reduce the total fluid volume variable as fluid is pumped to the heater bag line 128.

Fig. 14 is a flow diagram of a method 1400 for monitoring total fluid volume in a dialysate bag, according to some embodiments. It should be understood that method 1400 is described as being performed by PD system 100. More specifically, the various steps described below may be implemented by a processor such as the control unit 139 of the PD machine 102 configured to be able to execute a number of instructions. However, it should be understood that the method 1400 may be performed by any PD machine configured to be capable of draining fluid from the peritoneal cavity of a patient during a PD cycle. In various embodiments, the method 1400 may be implemented using hardware, software executed by a general purpose processor configured to be capable of controlling a special purpose device, such as a PD machine, or a combination of hardware and software.

At step 1402, a total fluid volume variable is initialized. In one embodiment, a variable may be initialized to store a value of zero. This variable is used to monitor the total amount of fluid drawn from the dialysate bag attached to the PD machine 102. In another embodiment, the variable may be initialized to store a value reflecting the initial volume of fluid in the dialysate bag. This variable is then used to monitor the estimated volume of fluid remaining in the dialysate bag.

At step 1404, the measured fluid volume for a single pump cycle is determined. In one embodiment, step 1404 includes method 1200 described above.

At step 1406, the measured fluid volumes are accumulated into a total fluid volume variable. In one embodiment, the measured fluid volume for a single pump cycle is added to the value stored in the total fluid volume variable. In another embodiment, the measured fluid volume for a single pump cycle is subtracted from the value stored in the total fluid volume variable. The selection of whether to subtract or add the incremental volume value for a single pump cycle to the value of the total fluid volume variable is based on a design choice for whether the value represents the volume of fluid drawn from the dialysate bag or the volume of fluid remaining in the dialysate bag.

At step 1408, the value of the total fluid volume variable is compared to a threshold value. In one embodiment, if the value of the total fluid volume variable is greater than the threshold, it is an indication that the dialysate bag may be nearly empty, and at step 1410, a refill cycle may be performed to refill the dialysate bag with fluid from the second dialysate bag. However, returning to step 1408, if the value of the total fluid volume variable is less than the threshold, this indicates that the dialysate bag may have sufficient fluid to continue the PD therapy, and at step 1412, the PD therapy may continue and another pump cycle returns to step 1404 to continue accumulating the incrementally measured fluid volume in the total fluid volume variable for the next pump cycle. Alternatively, at step 1412, when a new dialysate bag is connected to the PD machine 102, the PD therapy may be interrupted and the total fluid volume variable may be reset for the next PD therapy.

In another embodiment, at step 1408, if the value of the total fluid volume variable is less than the threshold, it is an indication that the dialysate bag may be nearly empty. In such embodiments, the threshold value may be substantially close to zero, and the total fluid volume variable may be initialized to a value representing an initial volume of the dialysate bag, with the incrementally measured fluid volume for each pump cycle subtracted from the total fluid volume variable.

FIG. 15 illustrates an exemplary computer system 1500 in accordance with some embodiments. It should be appreciated that, in various embodiments, the control unit 139 may be implemented at least in part as comprising components of the computer system 1500. As described above, the processor 1510 may execute instructions that cause the computer system 1500 to implement the functionality of the control unit 139.

As shown in fig. 15, the system 1500 includes a processor 1510, volatile memory 1520, non-volatile memory 1530, and one or more input/output (I/O) devices 1540. Each of the

components

1510, 1520, 1530, and 1540 can be interconnected, e.g., using a system bus 1550, to enable communication between the components. The processor 1510 is capable of processing instructions for execution within the system 1500. The processor 1510 may be a single threaded processor, a multi-threaded processor, a vector processor implementing a Single Instruction Multiple Data (SIMD) architecture, a quantum processor, or the like. The processor 1510 is capable of processing instructions stored in the volatile memory 1520. In some embodiments, the volatile memory 1520 is Dynamic Random Access Memory (DRAM). Instructions may be loaded from the non-volatile memory 1530 into the volatile memory 1520. In some embodiments, the non-volatile memory 1530 may include flash memory, such as EEPROM. In other embodiments, the non-volatile memory 1530 may include a Hard Disk Drive (HDD), a Solid State Drive (SSD), or other types of non-volatile media. The processor 1510 is configured to execute instructions that cause the PD machine 102 to perform the various functions described above.

In some embodiments, the memory 1520 stores information for the operation of the PD machine 102. For example, the operating parameters may be stored in the memory 1520. The processor 1510 may read the values of the operating parameters from the memory 1520 and then adjust the operation of the PD machine 102 accordingly. For example, the velocity of the

pistons

133A, 133B may be stored in the memory 1520 or written to and read from the memory 1520. This speed is then used to control the signal transmitted to the stepper motor driver.

I/O device 1540 provides an input and/or output interface for system 1500. In some embodiments, the I/O device 1540 includes a Network Interface Controller (NIC) that enables the system 1500 to communicate with other devices over a network, such as a Local Area Network (LAN) or a Wide Area Network (WAN), such as the internet. In some embodiments, the non-volatile memory 1530 may include both local and remote computer-readable media. Remote computer-readable media may refer to network storage devices such as a Storage Area Network (SAN) or cloud-based storage service. The I/O devices 1540 may also include, but are not limited to, serial communication devices (e.g., RS-232 ports, USB hosts, etc.), wireless interface devices (e.g., transceivers conforming to Wi-Fi or cellular communication protocols), sensor interface controllers, video controllers (e.g., graphics cards), or the like.

It should be understood that system 1500 is merely one exemplary computer architecture and that control unit 139 or other processing device may include various modifications, for example, in place of or in addition to the components shown in fig. 15. For example, in some embodiments, the control unit 139 may be implemented as a system on a chip (SoC) that includes a main integrated circuit die including one or more CPU cores, one or more GPU cores, memory management units, analog domain logic, or the like coupled to volatile memory, such as one or more SDRAM integrated circuit dies, stacked on top of the main integrated circuit die and connected in a single package (e.g., chip) via wire bonds, microsphere arrays, and the like. When connected to the SoC via a printed circuit board, the chip may be included in a chipset that includes additional chips that provide the functionality of the I/O device 1540.

For purposes of illustration, the systems and techniques described herein are primarily discussed in connection with a particular type of PD cycler, such as a PD cycler having a piston-based pump and a heater tray for batch-heating dialysate in a heater bag. It should be noted that the systems and techniques described herein may be suitably used in connection with other types and configurations of dialysis machines that involve transferring fluid to and from a patient via a patient line, and for which patient line checks and occlusion detection would be beneficially performed. For example, the systems and techniques described herein can be used in connection with PD cyclers that use different configurations and types of pumps, such as peristaltic pumps, and with other types of dialysate heating devices, such as in-line heating devices.

It should be noted that the techniques described herein may be embodied in executable instructions stored in a computer-readable medium for use by or in connection with a processor-based instruction execution machine, system, device, or apparatus. Those skilled in the art will appreciate that for some embodiments, various types of computer-readable media for storing data can be included. As used herein, "computer-readable medium" includes one or more of any suitable medium for storing executable instructions of a computer program, such that an instruction-executing machine, system, device, or apparatus can read (or retrieve) the instructions from the computer-readable medium and execute the instructions for performing the described embodiments. Suitable storage formats include one or more of electronic, magnetic, optical, and electromagnetic formats. A non-exhaustive list of conventional exemplary computer readable media includes: a portable computer diskette; random Access Memory (RAM); read Only Memory (ROM); erasable programmable read-only memory (EPROM); a flash memory device; and optical storage devices including portable Compact Discs (CDs), portable Digital Video Discs (DVDs), and the like.

It is to be understood that the arrangement of components shown in the figures is for illustrative purposes and that other arrangements are possible. For example, one or more of the elements described herein may be implemented in whole or in part as electronic hardware components. Other elements may be implemented in software, hardware, or a combination of software and hardware. Further, some or all of these other elements may be combined, some may be omitted altogether, and additional components may be added while still achieving the functionality described herein. Thus, the subject matter described herein can be embodied in many different variations, and all such variations are considered to be within the scope of the claims.

To facilitate an understanding of the subject matter described herein, many aspects are described in terms of sequences of actions. Those skilled in the art will recognize that various actions could be performed by specialized circuits or circuits, by program instructions being executed by one or more processors, or by a combination of both. The description herein of any sequence of actions does not imply that a particular order must be followed in order for the sequence to be performed. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the subject matter (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term "at least one" followed by a list of one or more items (e.g., "at least one of a and B") should be construed to mean the selection of one item from the listed items (a or B) or any combination of two or more of the listed items (a and B), unless otherwise indicated herein or clearly contradicted by context. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the scope of protection sought is defined by the claims as set forth below, and any equivalents thereof. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the subject matter and does not pose a limitation on the scope of the subject matter unless otherwise claimed. The use of the term "based on" and other similar phrases in the claims and in the written description to indicate the conditions that cause a result is not intended to exclude any other conditions that cause the result. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as claimed.

Claims

1. A dialysis system, comprising:

a plurality of pumps;

a cassette comprising a plurality of pump chambers, wherein each pump chamber is fluidly connected to a corresponding pressure chamber; and

a processor configured to be capable of:

the first pump is operated to draw fluid into a first pump chamber fluidly connected to the first pressure chamber,

measuring a first fluid volume in the first pump chamber;

operating the first and second pumps to transfer fluid from the first pump chamber to a second pump chamber fluidly connected to a second pressure chamber,

measuring a volume of a second fluid in the second pump chamber, an

Determining a measured fluid volume for a single pump cycle based on the first fluid volume and the second fluid volume.

2. The dialysis system of claim 1, wherein each pump comprises a piston configured to be engageable with a corresponding pump chamber to increase or decrease the volume of the corresponding pump chamber.

3. The dialysis system of claim 2, wherein measuring the volume of fluid in the corresponding pump chamber comprises:

extending the pistons to reduce the volume of the corresponding pump chambers;

monitoring a pressure signal from a pressure transducer configured to measure a fluid pressure in a corresponding pressure chamber;

reading a position of the piston at a time indicated by the pressure signal; and

converting the position of the piston into a measured fluid volume.

4. The dialysis system of claim 3, wherein the position of the piston is read based on an encoder signal for a lead screw attached to the piston.

5. The dialysis system of claim 1, wherein determining a measured fluid volume for a single pump cycle comprises:

determining a difference between the first fluid volume and the second fluid volume;

comparing the difference to a threshold; and

calculating an average of the first fluid volume and the second fluid volume as the measured fluid volume if the difference is below the threshold.

6. The dialysis system of claim 5, wherein determining a measured fluid volume for a single pump cycle further comprises:

setting an alarm if the difference is above the threshold.

7. The dialysis system of claim 5, wherein the threshold is equal to 10% of the volume of the first fluid.

8. The dialysis system of claim 1, wherein the plurality of pumps comprises at least three pumps and the processor is further configured to:

operating the second and third pumps to transfer fluid from the second pump chamber to a third pump chamber fluidly connected to a third pressure chamber;

measuring a third fluid volume in the third pump chamber; and

calculating an average of the first fluid volume, the second fluid volume, and the third fluid volume as the measured fluid volume.

9. The dialysis system of claim 1, wherein the fluid is a dialysis solution.

10. The dialysis system of claim 1, wherein fluid is drawn from a heater bag line coupled to the cartridge, and the processor is further configured to:

accumulating the measured fluid volume in a total fluid volume variable to monitor a total amount of fluid drawn from the heater bag line;

determining that a total amount of fluid drawn from the heater bag line is above a threshold; and

the cartridge is configured to draw fluid from the second line to transfer additional fluid to the heater bag line.

11. A method of operating a dialysis machine, the method comprising:

operating a first pump to draw fluid into a first pump chamber of a cassette, wherein the first pump chamber is fluidly connected to a first pressure chamber;

measuring a first fluid volume in the first pump chamber;

operating the first and second pumps to transfer fluid from the first pump chamber to a second pump chamber of the cassette, wherein the second pump chamber is fluidly connected to a second pressure chamber;

measuring a second fluid volume in the second pump chamber; and

12. The method of claim 11, wherein each pump chamber is engaged with a piston configured to increase or decrease the volume of the corresponding pump chamber.

13. The method of claim 12, wherein measuring the volume of fluid in the corresponding pump chamber comprises:

extending the pistons to reduce the volume of the corresponding pump chambers;

converting the position of the piston into the measured fluid volume.

14. The method of claim 11, wherein determining the measured fluid volume for a single pump cycle comprises:

comparing the difference to a threshold; and

15. The method of claim 14, wherein determining a measured fluid volume for a single pump cycle further comprises:

setting an alarm if the difference is above the threshold.

16. The method of claim 11, further comprising:

accumulating the measured fluid volume in a total fluid volume variable to monitor a total amount of fluid drawn from a heater bag line;

17. A non-transitory computer readable storage medium storing instructions that, when executed by a processor, cause a dialysis machine to measure fluid volume by performing steps comprising:

measuring a first fluid volume in the first pump chamber;

measuring a second fluid volume in the second pump chamber; and

18. The non-transitory computer readable storage medium of claim 17, wherein each pump chamber is engaged with a piston configured to be able to increase or decrease the volume of the corresponding pump chamber, and measuring the volume of fluid in the corresponding pump chamber comprises:

extending the pistons to reduce the volume of the corresponding pump chambers;

converting the position of the piston into the measured fluid volume.

19. The non-transitory computer readable storage medium of claim 17, wherein determining the measured fluid volume for a single pump cycle comprises:

comparing the difference to a threshold; and

if the difference is below the threshold, calculating an average of the first fluid volume and the second fluid volume as the measured fluid volume.

20. The non-transitory computer readable storage medium of claim 17, the steps further comprising: